In this article dedicated to a book about the Software Open Music developped at the Ircam, we explain our personal use of this software. In some cases, when the musical process is sufficiently verbalised and formalized, the computer allows the composer to concentrate on the music and to spend time on the calculation. We show a very simple example of technique used in the orchestral work Hérédo-Ribotes for viola solo and fifty-one orchestra musicians, and we illustrate the aesthetic ideas underlying this piece. We also show different cases in which the computer is a good musical assistant in the production of this esthetical meaning, and in which it is, on the contrary, better by hand.